Observation method and observation apparatus

ABSTRACT

In an observation method, measurement values of an object of measurement at a plurality of different positions in a plane that intersects a depth direction are acquired from an optical coherence tomography instrument (S100). In the observation method, measurement values are integrated in the depth direction at each of the plurality of positions (S104). In the observation method, a shrinkage parameter of the object of measurement is calculated on the basis of the integrated values at each of the plurality of positions (S105).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No.2018-175126, filed in the Japan Patent Office on Sep. 19, 2018, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to an observation method and anobservation apparatus.

BACKGROUND

Ceramics are excellent with respect to various physical properties, suchas hardness, heat resistance, corrosion resistance, and electricalinsulation. Consequently, ceramic structures fabricated to function asdemanded in a certain application are being used for a variety ofpurposes.

Ceramic structures are fabricated through steps performed on rawmaterial, such as a mixing step, a molding step, a drying step, and afiring step (see PTL 1). A ceramic structure being fabricated shrinksduring steps such as the drying step and the firing step. The structureafter shrinking is ground to fit a demanded size. The structure aftershrinking is hard, and grinding is time-consuming. For this reason, thesize of the structure before shrinking in the molding step (hereinafterreferred to as the “molded body”) is determined such that the structureis as close to the demanded size as possible after shrinking.

The shrinkage during the fabrication process varies depending on factorssuch as the properties of the molded body. Consequently, even with thesame mix, the size of the molded body to be determined varies with everybatch of mixed raw material. In the molding step of the related art, anintermediate molded body is molded with a rubber press or the like, ashrinkage ratio is estimated through inspection of the intermediatemolded body, the size of the molded body is determined on the basis ofthe shrinkage ratio, and the intermediate molded body is cut to matchthe size of the molded body. The inspection of the intermediate moldedbody takes a relatively long time. Consequently, a piece of theintermediate molded body made of raw material mixed from the same batchis extracted to inspect the intermediate molded body of the piece, andthe shrinkage ratio estimated on the basis of the inspection is treatedas the shrinkage ratio of the molded body from the same batch to adjustcutting conditions such as the cutting amount.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laid-Open No. 2017-170869

SUMMARY

An observation method according to a first aspect includes:

acquiring, from an optical coherence tomography instrument, measurementvalues of an object of measurement at a plurality of different positionsin a plane that intersects a depth direction;

calculating integrated values by integrating the measurement values inthe depth direction at each of the plurality of positions; and

calculating a shrinkage parameter of the object of measurement on abasis of the integrated values at each of the plurality of positions.

Also, an observation apparatus according to a second aspect includes

a controller that acquires, from an optical coherence tomographyinstrument, measurement values of an object of measurement at aplurality of different positions in a plane that intersects a depthdirection, calculates integrated values by integrating the measurementvalues in the depth direction at each of the plurality of positions, andcalculates a shrinkage parameter of the object of measurement on a basisof the integrated values at each of the plurality of positions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a function block diagram illustrating a schematicconfiguration of an observation system including an observationapparatus according to an embodiment;

FIG. 2 is a diagram illustrating the relationship between a measurementvalue and a depth direction calculated by a controller of the opticalcoherence tomography instrument in FIG. 1;

FIG. 3 is a diagram for explaining measurement values calculated at aplurality of positions by the optical coherence tomography instrument inFIG. 1;

FIG. 4 is a diagram for explaining how the controller of the observationapparatus in FIG. 1 aligns the depth positions that act as the peaks ofthe measurement values to a reference position;

FIG. 5 is a diagram for explaining how the controller of the observationapparatus in FIG. 1 calculates integrated values by integrating, in thedepth direction, measurement values detected at a plurality ofpositions;

FIG. 6 is a graph for explaining a calibration curve illustrating acorrespondence relationship between the integrated value of themeasurement values and the green density;

FIG. 7 is a diagram illustrating an example of parameters displayed onthe display in FIG. 1; and

FIG. 8 is a flowchart for explaining a map creation process executed bythe controller of the observation apparatus in FIG. 1.

DETAILED DESCRIPTION

Hereinafter, embodiments of an observation apparatus applying thepresent disclosure will be described with reference to the drawings.

As illustrated in FIG. 1, an observation system 11 that includes anobservation apparatus 10 according to an embodiment of the presentdisclosure is configured to include an optical coherence tomographyinstrument 12 and the observation apparatus 10. The observation system11 observes a molded body that is an intermediate body of a ceramicstructure as an object of measurement obj, for example. Note that inFIG. 1, the solid lines with arrowheads joining function blocksillustrate the advancement of beams of light. Also, in FIG. 1, thedashed lines joining function blocks illustrate the flow of controlsignals or communicated information. The communication indicated by thedashed lines may be wired communication or wireless communication.

The optical coherence tomography instrument 12 captures images from thesurface of the object of measurement obj to a maximum depth ofapproximately 10 mm by optical coherence tomography (OCT). In thepresent embodiment, the optical coherence tomography instrument 12 is awavelength-swept OCT apparatus, but may also be another type of OCTapparatus. The optical coherence tomography instrument 12 includes alight source 13, a beam splitter 14, a reference mirror 15, a scanner16, a detector 17, and a controller 18.

The light source 13 emits light in a band that is detectable by thedetector 17, such as light in the near-infrared band for example. Thelight source 13 may be a wavelength-swept light source, and mayrepeatedly emit light of a wavelength that changes within a preset rangealong the time axis. Note that in the configuration in which the opticalcoherence tomography instrument 12 is a type of OCT apparatus other thanthe wavelength-swept type, the light source 13 may be a light sourcecorresponding to that type. The light source 13 includes a collimatedlens for example, and emits collimated light having a narrow diameter.

The beam splitter 14 is provided in the emission direction of the lightsource 13. The beam splitter 14 is a half-mirror, for example. The beamsplitter 14 splits the light emitted from the light source 13, andcauses the light to advance in two directions. Additionally, the beamsplitter 14 causes coherent light obtained by mixing reference lightincident from the reference mirror 15 with signal light incident fromthe object of measurement obj to advance toward the detector 17.

The reference mirror 15 is provided in one of the advancement directionsof the light split by the beam splitter 14. The reference mirror 15 isdisposed such that the mirror plane is perpendicular to the advancementdirection, and reflects incident light toward the beam splitter 14 asreference light.

The scanner 16 scans the object of measurement obj by using the lightadvancing in a different direction from the reference mirror 15 out ofthe light split by the beam splitter 14 as irradiating light. Thescanner 16 may scan by any of various mechanisms. For example, thescanner 16 may use a reflective member such as a galvanometer mirror toscan by reflecting the irradiating light while changing the reflectiondirection. Additionally, the scanner 16 may also scan by using a movablestage to change the irradiated position of the irradiating light on thesurface of the object of measurement obj.

The scanner 16 may scan the object of measurement obj inside apredetermined region on an irradiated surface of the object ofmeasurement obj. The predetermined region may have a square shape, forexample. The object of measurement obj may be scanned by any of variousmethods, such as raster scanning, vector scanning, or spiral scanning,for example. In the embodiment, the object of measurement obj is scannedby raster scanning.

Note that the object of measurement obj is disposed so as to beirradiated with the irradiating light at an angle of incidence equal toor greater than 0° in the optical coherence tomography instrument 12.The irradiating light made to irradiate various positions of the objectof measurement obj by the scanner 16 advances in the depth directionfrom the surface while attenuating due to absorption, and is reflectedand scattered at each depth position. The reflected and scattered signallight is incident on the beam splitter 14.

The detector 17 receives the coherent light advancing from the beamsplitter 14. The detector 17 outputs a measurement signal having anintensity corresponding to the amount of received light.

The controller 18 includes one or more processors and memory. Theprocessor(s) may include a general-purpose processor that executesspecific functions by loading specific programs, and a special-purposeprocessor dedicated to a specific process. The special-purpose processormay include an application specific integrated circuit (ASIC). Theprocessor(s) may also include a programmable logic device (PLD). The PLDmay include a field-programmable gate array (FPGA). The controller 18may also be a system-on-a-chip (SoC) or a system in a package (SiP) inwhich one or a plurality of processors cooperate.

The controller 18 calculates the reflected light intensity in the depthdirection at any irradiated position EP of the irradiating light EL asillustrated in FIG. 2 by performing an inverse Fourier transform on themeasurement signal acquired from the detector 17 as a measurement value.The controller 18 recognizes the irradiated position EP in a planeintersecting the depth direction overlapping the radiation direction ofthe irradiating light EL by acquiring position information from thescanner 16. The controller 18 outputs the irradiated position EP and thereflected light intensity along the depth direction to the observationapparatus 10 in association with each other.

The observation apparatus 10 includes a controller 19, storage 20, and adisplay 21.

The controller 19 includes one or more processors and memory. Theprocessor(s) may include a general-purpose processor that executesspecific functions by loading specific programs, and a special-purposeprocessor dedicated to a specific process. The special-purpose processormay include an application specific integrated circuit (ASIC). Theprocessor(s) may also include a programmable logic device (PLD). The PLDmay include an FPGA. The controller 19 may also be a SoC or a SiP inwhich one or a plurality of processors cooperate.

As illustrated in FIG. 3, the controller 19 acquires a plurality ofdifferent positions in the plane intersecting the depth direction fromthe optical coherence tomography instrument 12, or in other words,measurement values of the object of measurement obj at a plurality ofirradiated positions EP. Note that in the present embodiment, ameasurement value of the object of measurement obj is the reflectedlight intensity along the depth direction, as described above. Thecontroller 19 may cause the storage 20 to store the acquired measurementvalues along the depth direction at each of the plurality of positions.

The controller 19 may detect the position in the depth direction where apeak occurs in the measurement value of the object of measurement obj ateach of the plurality of positions as a peak position. As illustrated inFIG. 4, the controller 19 may align a reference position in the depthdirection of the measurement values of the object of measurement obj ateach of the plurality of positions (for example, from a first irradiatedposition to a fifth irradiated position) to the detected peak position.

As illustrated in FIG. 5, the controller 19 integrates the measurementvalues in the depth direction at each of the plurality of positions tocalculate integrated values. Note that when calculating the integratedvalues, the controller 19 may integrate the measurement values includedwithin a range of a predetermined depth position. The range of thepredetermined depth position in the calculation of the integrated valuesmay be a range of a depth position in a coordinate system that takes areference point in the optical coherence tomography instrument 12 foreach of the plurality of positions as the origin, or a range of the samedepth position based on the peak position in the depth direction.

On the basis of the integrated values, the controller 19 calculates ashrinkage parameter of the object of measurement obj at each of theplurality of positions. Note that the shrinkage parameter is anyvariable expressing the internal state of the molded piece treated asthe object of measurement obj, which influences the degree of shrinkagewhen drying and firing the object of measurement obj. The shrinkageparameter is a parameter such as the green density or the porosity ofthe molded piece, for example. The integrated value is correlated with ashrinkage parameter such as the green density, which may vary dependingon the roughness or fineness of the molded piece. Accordingly, thecontroller 19 may calculate the shrinkage parameter by converting fromthe integrated value using a calibration curve of the shrinkageparameter with respect to the integrated value, like the one illustratedin FIG. 6 as an example.

As illustrated in FIG. 7, the controller 19 may create a parameter mapPM illustrating the shrinkage parameter calculated at each of theplurality of positions in association with the plurality of positions ina plane. Note that the controller 19 may create an integrated value mapillustrating the integrated value calculated at each of the plurality ofpositions in association with the plurality of positions in a plane.

The controller 19 reports the shrinkage parameter calculated at each ofthe plurality of positions to a ceramic structure fabrication apparatus.On the basis of the reported shrinkage parameter, the fabricationapparatus determines cutting conditions for the object of measurementobj for which the shrinkage parameter was calculated. The fabricationapparatus cuts the object of measurement obj under the determinedcutting conditions, and fabricates the ceramic structure by goingthrough a drying step and a firing step. Note that the controller 19 mayalso calculate the cutting conditions on the basis of the shrinkageparameter. In a configuration in which the controller 19 calculates thecutting conditions, the controller 19 controls the fabrication apparatusto cut the object of measurement obj according to the calculated cuttingconditions.

The storage 20 includes storage devices of any type, such as randomaccess memory (RAM) and read only memory (ROM), for example. The storage20 stores various programs causing the controller 19 to function, aswell as various information used by the controller 19.

The storage 20 stores the reflected light intensity along the depthdirection at each of a plurality of positions for each object ofmeasurement obj, for example. Additionally, the storage 20 stores acalibration curve of the shrinkage parameter with respect to theintegrated value, for example. Additionally, the storage 20 stores theshrinkage parameter calculated for each object of measurement obj ateach of the plurality of positions, for example.

The display 21 is a display that displays images, such as a liquidcrystal display or an organic EL display. The display 21 may display atleast one of the parameter map PM and the integrated value map createdby the controller 19.

Next, a map creation process executed by the controller 19 in theembodiment will be described using the flowchart in FIG. 8. The mapcreation process starts together when the optical coherence tomographyinstrument 12 starts measuring the measurement values of any object ofmeasurement obj. Note that the start of the measurement by the opticalcoherence tomography instrument 12 may be recognized by the controller19 through a synchronization signal acquired from the optical coherencetomography instrument 12, for example.

In step S100, the controller 19 acquires the measurement value of theobject of measurement obj, or in other words the reflected lightintensity along the depth direction, at any irradiated position EP.After the acquisition, the process proceeds to step S101.

In step S101, the controller 19 detects the position in the depthdirection where a peak occurs in the measurement value acquired in stepS100 as a peak position. After the detection of the peak position, theprocess proceeds to step S102.

In step S102, the controller 19 determines whether or not a measurementvalue has been acquired at all positions where the object of measurementobj is to be measured. Note that the controller 19 may determine whetheror not a measurement value has been acquired at all positions on thebasis of the synchronization signal acquired from the optical coherencetomography instrument 12, notification information indicatingcompletion, or the like. In the case where a measurement value has notbeen acquired at all positions, the process returns to step S100. In thecase where a measurement value has been acquired at all positions, theprocess proceeds to step S103.

In step S103, the controller 19 aligns a reference position in the depthdirection of the measurement values at each of the plurality ofpositions to the peak position detected in step S101. After thereference positioning, the process proceeds to step S104.

In step S104, the controller 19 integrates the measurement values withina range of a predetermined depth position aligned with the referenceposition in step S103 to calculate integrated values. After thecalculation of the integrated values, the process proceeds to step S105.

In step S105, the controller 19 calculates a shrinkage parameter at eachof the plurality of positions on the basis of the integrated valuescalculated in step S104. After the calculation of the shrinkageparameters, the process proceeds to step S106.

In step S106, the controller 19 creates a parameter map PM and anintegrated value map illustrating the shrinkage parameters and theintegrated values at each of the plurality of positions calculated insteps S104 and S105, respectively. After the creation of the parametermap PM and the integrated value map, the process proceeds to step S107.

In step S107, the controller 19 causes the display 21 to display theparameter map PM and the integrated value map created in step S106.After the displaying of the parameter map PM and the integrated valuemap, the process proceeds to step S108.

In step S108, the controller 19 outputs the integrated value map and theparameter map PM created in step S106 to the fabrication apparatus.After the output of the integrated value map and the parameter map PM,the map creation process ends.

In the observation apparatus 10 according to the present embodimenthaving a configuration like the above, measurement values of the objectof measurement obj measured at a plurality of positions by the opticalcoherence tomography instrument 12 are used. Consequently, because theobservation apparatus 10 uses a measurement result from the opticalcoherence tomography instrument 12 which is capable of fast andnon-invasive imaging, the observation apparatus 10 is capable of fastobservation of each object of measurement obj that is ultimatelyprocessed into a finished product.

Also, the observation apparatus 10 according to the embodimentintegrates, in the depth direction, the measurement values andcalculates a shrinkage parameter of the object of measurement obj on thebasis of the integrated values at each of a plurality of positions.According to such a configuration, the observation apparatus 10 maydetect a parameter that influences shrinkage in steps such as the dryingstep and the firing step at each of the plurality of positions.Consequently, the observation apparatus 10 may provide parameters thatmay be used to determine fabrication conditions such as the localtemperature and humidity in at least one of the drying step and thefiring step.

Also, the observation apparatus 10 according to the embodiment displaysat least one of the parameter map PM and the integrated value map.According to such a configuration, the observation apparatus 10 mayenable an operator to visualize the internal state at each of aplurality of positions in the object of measurement obj.

Also, the observation apparatus 10 according to the present embodimentintegrates the measurement values within a range of a predetermineddepth position. With the resolving power of an optical coherencetomography instrument, the surface of the object of measurement obj maybe detected with one or two pixels, or in other words at one or twodepth positions, respectively. A measurement value obtained by detectingthe surface of the object of measurement obj with one pixel is greatlydifferent in intensity from a measurement value detecting with twopixels. Therefore, an average value of the measurement values at a depthposition corresponding to the surface where the intensity isparticularly strong has relatively low reliability as a measurementvalue. On the other hand, the observation apparatus 10 having theconfiguration described above may integrate the measurement valueswithin a range that excludes the depth position corresponding to thesurface, and therefore may improve the estimation accuracy for theshrinkage of the object of measurement obj based on the shrinkageparameter.

Also, the observation apparatus 10 according to the embodiment performsthe integration with respect to the measurement values at the same depthposition with reference to the peak position. In the optical coherencetomography instrument 12, the surface of the object of measurement isinclined with respect to the advancement direction of the irradiatinglight, or in other words the depth direction, to reduce the detection ofstrong back-reflections from the surface of the object of measurement.The irradiating light EL that irradiates the object of measurement objattenuates greatly as the irradiating light EL advances in the depthdirection from the surface, and consequently, the intensity of themeasurement values also drops as the depth position from the surfacebecomes longer. With respect to such a phenomenon, the observationapparatus 10 having the configuration described above integrates themeasurement values at the same depth positions with reference to thepeak position estimated as the surface position at each of a pluralityof positions, and therefore may calculate a shrinkage parameter limitedto a range that greatly influences shrinkage at each of the plurality ofpositions, even with a configuration in which the object of measurementobj is inclined with respect to the depth direction.

Also, in the observation apparatus 10 according to the embodiment, theintegrated value is converted to a shrinkage parameter by using acalibration curve. Consequently, the observation apparatus 10 may reducethe processing load on the controller 19.

The present disclosure has been described on the basis of theaccompanying drawings and examples, but it should be noted that variousmodifications and alterations may be performed easily by persons skilledin the art on the basis of the present disclosure. Consequently, itshould be noted that these modifications and alterations are included inthe scope of the present disclosure.

Although the foregoing discloses a system described as including variousmodules and/or units that execute specific functions, it should be notedthat these modules and units are illustrated schematically to brieflydescribe their functionality, and do not necessarily indicate specifichardware and/or software. In this sense, it is sufficient for thesemodules, units, and other structural elements to be hardware and/orsoftware implemented to substantially execute the specific functionsdescribed herein. The various functions of different structural elementsmay be combined or separated into hardware and/or software in any way,and each can be used individually or in some combination with eachother. Furthermore, devices such as a keyboard, display, touchscreen,and pointing device are included, but inputs/outputs, I/O devices, or auser interface not limited to the above can be connected to the system,either directly or via an intervening I/O controller. In this way,various aspects of the content disclosed herein can be carried out inmany different modes, and these modes are all included in the scope ofthe content disclosed herein.

REFERENCE SIGNS LIST

-   10 observation apparatus-   11 observation system-   12 optical coherence tomography instrument-   13 light source-   14 beam splitter-   15 reference mirror-   16 scanner-   17 detector-   18 controller-   19 controller-   20 storage-   21 display-   EL irradiating light-   EP irradiated position-   obj object of measurement-   PM parameter map

The invention claimed is:
 1. An observation method comprising:irradiating a light beam to a first point of a green compact; separatinga first coherent light from reflected light at the first point using abeam splitter; measuring a first intensity of the first coherent light;calculating a first integrated value by integrating the first intensityin a depth direction; and calculating a first shrinkage parameter,comprising at least one of green density or porosity of the greencompact, based on the first integrated value.
 2. The observation methodaccording to claim 1, further comprising: displaying a parameter mapthat illustrates shrinkage parameters, including the first shrinkageparameter, wherein each of the shrinkage parameters is calculated ateach of a plurality of points of the green compact.
 3. The observationmethod according to claim 1, wherein the calculating of the firstintegrated value includes integrating the first intensity within a rangeof a predetermined depth position.
 4. The observation method accordingto claim 3, further comprising: detecting a peak position in the depthdirection of the first intensity at each of the plurality of points ofthe green compact, wherein the calculating of the first integrated valueincludes integrating the first intensity within a range of a depthposition with reference to the peak position.
 5. The observation methodaccording to claim 1, wherein the first shrinkage parameter is convertedfrom the first integrated value using a calibration curve.
 6. Theobservation method according to claim 1, further comprising: displayingan integrated value map that illustrates integrated values, includingthe first integrated value, calculated at a plurality of points of thegreen compact.
 7. The observation method according to claim 1, furthercomprising: irradiating the light beam to a second point of the greencompact; separating a second coherent light from the reflected light atthe second point using the beam splitter; measuring a second intensityof the second coherent light; calculating a second integrated value byintegrating the second intensity in the depth direction; and calculatinga second shrinkage parameter comprising at least one of green density orporosity of the green compact based on the second integrated value. 8.An observation apparatus comprising: a light source; a light splitter; adetector; and a controller communicatively connected to the lightsource, the light splitter, and the detector, the controller configuredto cause the light source to emit a light beam to irradiate a greencompact, cause the light splitter to separate coherent light fromreflected light, cause the detector to measure intensities of thecoherent light in a depth direction, calculate an integrated value byintegrating the intensities, and calculate a shrinkage parameter,comprising at least one of green density or porosity of the greencompact, based on the integrated value.